1. Field of the Invention
The present invention relates to a flame retardant that is hardly toxic and does almost no harm to the property of a polymer and also relates to a polymer composition including such a flame retardant.
2. Description of the Related Art
A polymer, as well as wood, is classified among flammables. For that reason, when a polymer should not burn in some application, the polymer cannot be used as it is, and the flammability of the polymer must be reduced in some way or other.
As used herein, the “polymers” (which will also be herein referred to as “resins” or “plastics”) refer to not only thermoplastic polymers but also thermosetting polymers as well. Also, a “polymer composition” will herein refer to a mixture of a polymer and another material (such as an inorganic filler).
Generally speaking, the flammability of a polymer is minimized by adding any of various types of flame retardants to the polymer or by introducing a substituent group into the backbone of the polymer. The flame retardants are roughly classifiable into halogen-based flame retardants and non-halogen-based flame retardants.
However, it is already known that halogen-based flame retardants on fire emit harmful acidic gases of hydrogen bromide or hydrogen chloride, for example. Also, it was recently discovered that the halogen-based flame retardants burning might produce dioxin, which is seriously harmful to the creatures and environments on the earth. In view of these problems, non-halogen-based flame retardants have been researched and developed lately as alternatives to the halogen-based flame retardants.
Examples of those non-halogen-based flame retardants include metal hydroxides or phosphides. The gas emitted from a flame retardant of a metal hydroxide such as magnesium hydroxide on fire is much less toxic than that emitted from a halogen-based flame retardant. However, the metal hydroxide flame retardant is not so flame-retarding as the halogen-based flame retardant. Accordingly, to increase the inflammability of a polymer with a metal hydroxide, the metal hydroxide must be added in profusion to the polymer, thus potentially deteriorating the property of the polymer.
A flame-retarding polymer composition, in which a sulfate of a triazine compound is added to a thermoplastic polymer, is disclosed as a non-halogen-based flame retardant in Japanese Laid-Open Publication No. 8-48812. The flame-retarding effects of this composition are fair enough but are still insufficient. Thus, the development of flame retardants and flame-retarding polymer compositions having even better flame-retarding effects is awaited.
Also, from the viewpoint of global environmental protection, natural resources such as petroleum are on the verge of exhaustion and the greenhouse effect, which is partially caused by the incineration of non-materially-recyclable or non-chemically-recyclable polymers disposed, has become more and more serious. To overcome these problems, biodegradable polymers have been researched and developed increasingly actively. Among other things, biodegradable polymers, which are produced from biomass, not fossil resources such as petroleum, have been developed particularly vigorously. More specifically, botanical biomass such as corns or potatoes is the object of much attention. This is because even though these materials generate carbon dioxide when burned, the materials can also immobilize the carbon dioxide that has been emitted to the air at relatively short cycles (e.g., in one year or so). Thus, these materials may be regarded as not contributing to the greenhouse effect in the long run.
As described above, the development of flame retardants and flame-retarding polymers, which do not emit any toxic gas such as dioxin, do almost no harm to the property of polymers and yet exhibits sufficient flame-retarding effects, is awaited. Furthermore, nobody has ever developed the technique of making a flame retardant from biomass or adding biodegradability to the flame retardant itself.